Acetylcholine receptors are involved in the modulation of a variety of physiological and behavioral functions, including neuroendocrine function, respiration, mood, motor control and function, focus and attention, concentration, memory and cognition, and substance abuse. Ligands for acetylcholine receptors have been demonstrated to have effects on attention, cognition, appetite, substance abuse, memory, extrapyramidal function, cardiovascular function, pain and gastrointestinal motility and function. The distribution of acetylcholine receptors that bind nicotine, i.e., nicotinic acetylcholine receptors, is widespread in the brain. In the periphery, acetylcholine receptors are found in muscle, autonomic ganglia, the gastrointestinal tract and the cardiovascular system (see, e.g., U.S. Pat. No. 5,594,011).
Acetylcholine receptors have been shown to be decreased, among other things, in the brains of patients suffering from Alzheimer's disease, and Parkinson's disease, as well as diseases associated with dementia, motor dysfunction and cognitive impairment. Such correlations between acetylcholine receptors and nervous system disorders suggest that compounds that modulate acetylcholine receptors will have beneficial therapeutic effects for many human nervous system disorders. U.S. Pat. No. 5,594,011 to McDonald et al., assigned to SIBIA Neuroscience, describes compounds such as SIB-1508Y that modulate nicotinic acetylcholine receptors. Such compounds are useful for, among other things, the treatment of Parkinson's disease. See also U.S. Pat. No. 5,723,477 to McDonald et al. Unfortunately, nicotine analogs are difficult compounds to synthesize, and there is a continuing need for new methods of making the same, as well as intermediates useful for the synthesis of nicotine analogs.
Y. Kondo et al., J Am. Chem. Soc. 121, 3539–3540 (1999), describe TMP-Zincate as a chemoselective base for directed ortho-metalation of certain aromatic and heteroaromatic compounds, along with the subsequent iodination thereof. P. Gros et al., J. Org. Chem. 67, 234–237 (2002), describe the lithiation of 2-heterosubstituted pyridines with BuLi-LiDMAE. However, neither reference describes or suggests the halogenation of nicotine or nicotine analogs.